An additional and important advantage of the polyethylene composition of the present invention is that it can be melt-processed at unusually high shear rate values, which mean high processing speeds and/or reduced melt-processing temperatures, without encountering flow-instabilities which generally produce unacceptable defects in the formed articles (e.g. shark skin or melt-fracture), even in the absence of processing aids.
Moreover, the fast crystallization kinetics of the present composition, which provides a critical contribution to its superior process-ability, also provides an unusually reduced shrinkage of the formed articles, thus allowing achieving a remarkable dimensional stability. Thus the composition of the present invention provides an unmatched balance of mechanical properties and process-ability with respect to the known polyethylene compositions for the same use, as disclosed in particular in U.S. Pat. No. 6,201,078.
In fact, the problem of achieving a high impact resistance, reducing the flow-instabilities and improving the dimensional stability (lowering shrinkage) is not mentioned in such document.